Meiosis

Form gametes with half the number of chromosomes, therefore at fertilisation can create an embryo with full set of chromosomes.

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Mitochondria

The inner of its two membranes is folded to form finger - like projections called cristae. The mitochondra are the site of the later stages of aerobic respiration.

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Test of totipotent plants

Small pieces of plant (explants) are surface sterelised and then placed on solid agar medium with nutrients and growth regulators.

By altering the growth regulators, cells of callus can be made to differentate to form small groups of cells. These embryos develop into complete plants that are genetically identicle clones.

-------------------------------------------------------------------------------------------------------- Stem Cell - undifferentied cells which are found in embryos and some are found in adults. Blood stem cells are found in the bone marrow and can develop into the various types specialised cells found in the blood.

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Microfibrils and Tyrosinase

Microfibrils

In the cell wall, layers of cellulose microfibrils are criss - crossed at different angles and are stuck together with a polysaccharide glue composed of short, branched polysaccharide known as hethicelluloses and pectins.

Tyrosinase

To make melanin, animals use an enzyme called Tyrosinase. This catalyses the first step along a chemical pathway, changing the amino acid tyrosinase into melanin.